In the field of architecture, we are witnessing the development of vibration dampers for absorbing the vibrations caused by earthquakes, typhoons, etc. to thereby incorporate a very efficient damping mechanism in buildings. Damping materials for vibration dampers are required to be high in damping capacity in order that the impact displacement and vibrations of the framework structural members of buildings may be absorbed and, at the same time, small in the temperature dependence of rigidity at and around room temperature in consideration of environmental conditions.
While materials of high molecular weight generally show high damping capacities in the neighborhood of glass transition temperature (Tg), this Tg region is the temperature region where such a high molecular material undergoes a transition from a highly rigid glass-like state to a sparingly rigid rubbery state and is also a region of high temperature dependence of rigidity. Therefore, it is usual that damping materials for general use are used at and around the glass transition temperature so as to let them express high damping capacities [Vibration Damping Technology, The Japan Society of Mechanical Engineers (ed.) Yokendo, p. 75].
In the architectural field, where changes in atmospheric temperature from summer months to winter months and vice versa and regional differences in atmospheric temperature, it is essential to avoid using damping materials having a large temperature dependence of rigidity. However, high damping capacities can hardly be expected at temperatures outside the glass transition temperature region, where the temperature dependence of rigidity is small. Thus, a small temperature dependence of rigidity and a large damping capacity are conflicting characteristics in polymer materials and usually it is extremely difficult to reconcile these two parameters.
Ordinary rubber materials have a certain degree of damping capacity at and around room temperature but if an attempt is made to increase the damping capacity, the rigidity will be sacrificed, with the result that, as a practical problem, the down-sizing of dampers are difficult. Moreover, these materials are hardly capable of providing a high damping capacity enough to use for dampers.
As damping rubbers exhibiting high damping capacities at and around room temperature, oil-modified norbornene rubbers and high-vinyl styrene-isoprene block copolymers and their hydrogenated versions (HYBLAR™), among others, are commercially available. These damping rubbers generally have glass transition points (Tg) at and around room temperature. Such materials have high damping capacities at and around room temperature but show large changes in elastic modulus around Tg so that the temperature dependence of rigidity at and around room temperature is very large, making them hardly applicable to dampers.
As damping materials for viscoelastic dampers in the architectural field, polyurethane compounds and polyurethane/asphalt compositions are known (Japanese Kokai Publication Hei-10-330451). However, all such materials remain to be further improved in regard of the balance between damping capacity and temperature-dependence of rigidity at and around room temperature. Particularly because the Tg of such a composition is designed to be not over 0° C. in order to minimize the temperature dependence of rigidity at and around room temperature, the damping capacity in the temperature region of about 20 to 40° C. is unduly low.
On the other hand, it is disclosed in WO 93/14135 and Japanese Kokai Publication Hei-7-137194 that damping materials may be obtained from styrene-isobutylene block copolymers but all that is disclosed there is that only general-purpose damping materials may be obtained and neither disclosure includes teachings on applications demanding special characteristics such as those required of viscoelastic dampers for use in the field of architecture. Moreover, in the materials specifically described as examples in the above publications, the glass transition temperature is invariably below −15° C. so that the temperature dependence of rigidity is small at and around room temperature. However, the damping capacities of these materials at and around room temperature are too low for them to use as damping materials.
In addition, the damper material composition for vibration dampers materials must have a rigidity of the order retaining its shape and a deformability capable of with standing large seismic vibrations due to an earthquake.
The technology of fabricating vibration dampers from such damping materials includes the method comprising laminating a damper sheet with steel plates using an adhesive and the hot-melt method comprising melt-molding the damping material. The laminating method using an adhesive is suitable for the processing of damping materials in the sheet form but does not easily lend itself to the fabrication of other shapes. Therefore, the damper material composition for vibration dampers preferably has self-adhesive properties. On the other hand, the hot-melt method comprises merely pouring a molten viscoelastic material into molds so that the material can be easily processed into a variety of shaped products, with the additional advantage that the processing cost is low. From these points of view, the damping materials for vibration dampers preferably have hot-melt properties.